A division of signals of the type described above is required for localization of radiation fields utilizing detector systems which can pick up radiation from the field simultaneously, namely, so-called localizing detector systems. By the provision of such detectors which simultaneously pick up radiation from the fields, it is possible to significantly shorten measuring times for localization of points in the radiation field with respect to operations with individual detectors which may be driven in a column-and-row format as is the case, for example, with thyroid gland scans in medicine.
It is known, for example, to provide multiple sources of radiation or radioactive implants with appropriate detectors for effecting a thyroid gland scan utilizing techniques relating to a radionuclide imaging, tomography, emission-computed tomography and the like. An example of a detector system for determining locality by simultaneously picking up radiation at a field from a plurality of detectors is the Anger camera for radiation fields, utilized in medicinal diagnostics.
A particular field of use for location-determining detectors is the field of scientific and technological research utilizing directed or non-directed radiation, for example for the reconstruction of three-dimensional images from two-dimensional sections provided by two-dimensional tomography in nondestructive testing and evaluation of materials and bodies.
The signal processing for all location-determining detector system's involves pulse division.
This can be effected separately with analog dividers and analog-to-digital converters provided at the outputs of the analog dividers or by numerical division following digitization of the dividend and divisor signals. Both processes are, however, relatively slow and expensive since the analog process requires pulse stretchers and the numerical process requires hard-wired calculators or computers.
Another type of signal processing in which the division and digitalizaton can be effected in a single step can be carried out in principle with a dividing analog-to-digital (ADC) whose reference potential is proportional to the signal level of the divisor and is modified to always be proportional to the signal level of the divisor.
When a dividing ADC is used in accordance with the Wilkinson process, excellent differential linearity is obtained. However, the process is relatively slow since the divisor signal may be subjected to a stretcher.
If division is carried out using an ADC operating in accordance with the principles of the successive approximation process, a stretching of the divisor signal is still required. As a consequence, the process is also slow. In addition, the differential linearity .+-.1/2 LSB (least significant bit) is poor. In principle, the fastest ADC is a parallel ADC (Flash) which can generate simultaneously n-bit digital information with 2.sup.n -1 comparators. If such an ADC is operated as a divider, no stretcher is required and as a consequence, the division-digitalization process is extremely fast. However, the differential linearity with .+-.1/2 LSB is unacceptable.
An averaging process utilizing an ADC is described in the prior art (see Cottini et al, A New Method for Analog to Digital Conversion, Nuclear Instruments and Methods, Vol. 24 (1963), pages 241-242) primarily for ADCs utilizing successive approximation principles whereby for multiple channel analyzers, a relatively short pulse-height-independent deadtime with good differential linearity will result.
The relatively short pulse-height-independent deadtime guarantees that a successive approximation process can be effected and the requisite good linearity achieved. For dividing ADCs, however, this process cannot be used.